1. Field of the Invention
The present invention relates generally to containers and, more particularly, to 55 gallon drums molded of cross-linked polyethylene which drums are suitable for shipment in interstate commerce on common carrier equipment.
2. Description of the Prior Art
Numerous attempts have been made to utilize synthetic polymeric materials in shipping containers for liquids and other substances. Polymeric materials, hereinafter called plastics, have certain potential advantages as shipping containers. Plastics are relatively resistant to many chemicals, such as acids and alkalis, which easily corrode most metals. In addition, because plastics are inherently lighter than metals, plastic drums have a lower shipping weight than conventional steel drums. Unfortunately, however, plastics by and large do not possess the necessary structural strength to withstand the rigors of use in common commercial carriers.
Before any plastic drum can be sold for common carrier usage, it must meet the rigorous federal regulations set forth in 49 CFR 178.19 governing polyethylene plastic containers. These regulations provide, inter alia, that plastic drums be able to withstand various compression loads based on the capacity of the drum. At the present time, these regulations only cover drums ranging in capacity from 21/2 gallons to 30 gallons, although a standard for 55 gallon plastic drums has recently been proposed. Prior to our invention no drum has yet been manufactured which passes all the proposed federal regulations for 55 gallon plastic drums and, in addition, is capable of being handled using all conventional drum handling equipment.
Attempts have been made to prepare plastic drums ranging up to 55 gallons in capacity. Such attempts have largely been unsuccessful because the drums either lacked the necessary compression strength, load temperature impact strength, or have been so difficult to handle using the ordinary drum handling equipment available to common carriers as to be commercially unacceptable.
U.S. Pat. Nos. 3,927,790 to Chase et al and 3,940,011 to Dubois et al disclose attempts to manufacture various 55 gallon plastic drums capable of being handled by conventional drum handling equipment. These patents depict generally keg-shaped drums having a plurality of flat sides or slots adapted to be engaged by a conventional forklift. Similarly, U.S. Pat. No. 3,889,939 to Simon et al discloses a plastic drum having slots on opposite sides of the drum engageable by a forklift and a ring or a slot on the top of the drum for handling by a standard handtruck.
All such keg-shaped or slotted drums, however, are not easily handled with conventional drum handling equipment because the handling equipment must be carefully positioned with respect to the drum so that the equipment will engage the flat sides, slots or other engaging paraphernalia. In practice, a worker using a forklift or a standard handcart will often be required to manually rotate the drum into the exact position necessary for handling before using the lift or handcart. Because a 55 gallon drum filled with liquid is extremely heavy and difficult to handle, such drums have not received great commercial acceptance because of the extra labor and time involved in orienting them to receive the drum handling equipment.
Furthermore, although attempts have been made to design plastic drums capable of being handled by a forklift and a standard handtruck, to the best of our knowledge, no such plastic drum has ever been capable of also being handled by use of the device known in the cargo industry as the "parrot beak". "Parrot beak" equipment is drum handling equipment which lifts a conventional steel drum using a jaw-like device which attaches to the top chime or bead of the drum, the chime or bead thereby bearing virtually all the weight of the drum. Typical of "parrot beak" drum handling equipment is the LIFT-O-MATIC Model PTA-720 of Marvel Industries, Inc., Evanston, Illinois.
Various prior art plastic drums, such as that shown in U.S. Pat. No. 3,889,939 disclose polyethylene drums made by a process called "blow molding". Blow molded drums are inherently uneven in thickness and, being thicker in the ends and top and thinner at the rolling hoops, often fail in the compression testing mandated by the applicable government regulations. Moreover, when fully loaded blow molded drums are stacked on top of each other, the lower drums tend to cave in.
Attempts have been made in the past to prepare drums using the rotational molding process. Such drums inherently have the same thickness throughout and, when properly designed, do not fail in compression. One such drum currently being marketed comprises a multilayer laminate having a thin skin of cross-linked, high density polyethylene, a foam core of a second plastic and an inner skin of a different material. However, this multilayer drum is not designed for easy handling using forklift or handtruck equipment and cannot be handled by "parrot beak" equipment.
Drums have been prepared using a single thickness of rotationally molded, cross-linked, high density polyethylene. Although these drums were provided with rolling hoops on the sides, the hoops could not support the weight of a fully loaded drum when engaged by the forks of a forklift truck. In addition, while various designs for the drum top or head were used or experimented with (one experimental model included slots in the top which could accommodate flanges on drum handling handtrucks), these drums could not be handled by "parrot beak" equipment.